Characterization Of Nitrobenzene And Aniline Degrading By Aerobic Granular Sludge

Nitrobenzene and aniline, widely used industrial chemicals, are two important nitroaromatic compounds that have been listed as priority pollutants for their nature of chemical stability, high toxicity, resistant to degradation and potential of accumulation in organism.With the development of chemical industry, China’s demand for nitrobenzene and aniline will continuously increase, and their wrongly handled and disposed of endanger both human and environmental health. Thus, the degradation of nitrobenzene and aniline is of great concern. Microbial degradation has obvious advantages in treatment of wastewater, gases and soil that containing nitrobenzene and aniline. These microorganism can utilize nitrobenzene or aniline as carbon source, nitrogen source or energe source for their growth and reproduce.Due to the chemical stability, however, benzene ring is hard to be opened by oxidation of oxygen. Thus, nitrobenzene and aniline are difficult to be mineralized. On the other hand, symmetry and stability of benzene ring also makes them hard to be degraded by biochemical reactions. Besides, nitrobenzene and aniline have great biological toxicity.This paper presents the latest research reports about the biodegradation of nitrobenzene and aniline, which include the screening and domestication of degrading microbes, the degradation pathways and degradation mechanism. Furthurmore, this paper emphasizes the importance of the development and application of engineering strains, and introduce the mineralization of nitrobenzene and aniline by mixed microbes and the application of granular sludge in the treatment of municipal wastewater.The highly efficient nitrobenzene/anline-degrading aerobic microbes were screened and domesticated from activated sludge and sediments from a nitrobenzene wastewater treatment plant. During the domestication processes, the mixed microbes formed granular sludge. Based on these mixed microbes, we studied the aerobic biodegradation of benzene and aniline.Bacteria(NB1), bacillus(NB2) and filamentous Bacteria(NB3) as well as yeast(AN1), bacillus(AN2) and filamentous Bacteria(AN3) are screened and purified from the mixed nitrobenzene-degrading bacteria and aniline-degrading bacteria, respectively. Besides the degradation effect of nitrobenzene or anline by each microorganism, their combined degradation effect in the treatment of corresponding nitroaromatic compounds has also been studied.The result show that the mixed nitrobenzene-degrading microbes degraded nitrobenzene most efficiently in the conditions with nitrobenzene as sole carbon and nitrogen source. The optimum condition for growth of the mixed microbes and degradation of nitrobenzene was 28℃and pH 7.0, and weak alkaline environment with pH below 9.0 is suitable for their growth.When nitrobenzene concentration was 600 mg/L, the mixed microbes can quickly adapt the environment in 6h, and they can completely degraded nitrobenzene in 24h, the maximum degradation rate could reach as high as 28.8 mg·(L·h)-1Similarly, the mixed anline-degrading microbes that cultivated in the environment with aniline can degraded aniline more efficiently in the conditions with aniline as sole carbon and nitrogen source than in the conditions with other carbon source and nitrogen source. The optimum condition for growth of the mixed microbes and degradation of aniline was 28℃and pH 7.0, and the environment with pH between 6.0 and 9.0 is suitable for their growth. When aniline concentration was 600 mg/L, the degradation rate could reach 33.6 mg (L·h)-1, and aniline can be completely degraded within 18 h.The results obtained from the experiments undergoing with pure microbes show that Bacteria(NB1) is the dominant bacteria among the nitrobenzene-degrading microbes. The conversion rate and mineralization rate of nitrobenzene by NB1 within 36 h can reach 56% and 41%, respectively.Among the aniline-degrading microbes, yeast(AN1) was the dominant bacteria. The conversion rate and mineralization rate of aniline by ANl within 36 h can reach 68% and 59%, respectively.The biodegradation results show that the mixed microbes degraded corresponding nitroaromatic compounds more efficiently than pure bacteria. It was suggested that there was an obvious synergistic effect among nitrobenzene-degrading bacteria as well as aniline-degrading bacteria, but no obvious synergistic effect or antagonism exists between nitrobenzene-degrading bacteria and aniline-degrading bacteria.No granular sludge formed in the mixed nitrobenzene-degrading microbes, which, however, appeared in the mixed aniline-degrading microbes in which the dominant bacteria was yeast(AN1). The OD600 of the mixed nitrobenzene-degrading microbes(N123) that consisted of Bacteria(NB1), bacillus(NB2) and filamentous Bacteria(NB3) was 0.43 within 36 h, and the degradation rate of nitrobenzene then was 84%.Similarly, The mixed aniline-degrading microbes(A123) that consisted of yeast(AN1), bacillus(AN2) and filamentous Bacteria(AN3) shows high aniline degradation rate. The OD600 of them within 36 h was 0.94, and the degradation rate of aniline reached 89%.The main reason for the formation of sluge granulation in biodegradation of nitrobenzene and aniline was the filamentous Bacteria multiply, and the secretion of extracellular polymer substances by yeast can explain why it is easier for the formation of sluge granulation in aniline degradation process than in nitrobenzene degradation process. Aerobic granular sludge is a new attempt to treat nitroaromatic compounds wastewater, and has very important practical value.